The present invention relates to instruments and methods for preparing adjacent bone structures, and more particularly, to instruments and methods for preparing adjacent vertebral endplates prior to a spinal fusion procedure.
Advancing age, as well as injuries, can lead to changes in the various bones, discs, joints and ligaments of the body. In particular, these changes can manifest themselves in the form of damage or degeneration of an intervertebral disc, the result of which is mild to severe chronic back pain. Intervertebral discs serve as xe2x80x9cshockxe2x80x9d absorbers for the spinal column, absorbing pressure delivered to the spinal column. Additionally, they maintain the proper anatomical separation between two adjacent vertebra. This separation is necessary for allowing both the afferent and efferent nerves to exit and enter, respectively, the spinal column.
Treatment for a diseased or damaged disc can involve the removal of the affected disc and subsequent fusion of the opposing vertebra to one another. Spinal fusion consists of fusing the adjacent vertebrae through the disc space (the space previously occupied by the spinal disc interposed between the adjacent vertebral bodies). Typically, a fusion cage and/or bone graft is placed into the disc space to position the vertebrae apart so as to create more space for the nerves, to restore the angular relationship between the adjacent vertebrae to be fused, and to provide for material that can participate in and promote the fusion process.
In general, the ability to achieve bone fusion appears to be related to certain factors, such as the quality and quantity of bone graft material present, the surface area available for the fusion to occur over, and the stability of the construct being fused. The fusion cage and/or bone graft should, for example, occupy a significant portion of the disc space to provide a large surface area over which fusion can occur, and should contour the vertebral endplates adjacent the disc space to provide stability and further promote fusion. The fusion cage and/or bone graft used for the purpose of interbody fusion, however, can not always be shaped to precisely fit the complex contours of the vertebral endplates adjacent the disc space. Accordingly, rather than shaping the fusion cage to contour the disc space, procedures have been developed for removing at least a portion of the outermost layer of the vertebral endplates. This is effective to cause bleeding to occur, and thereby to encourage the fusion and invoke the healing process of the bone.
Since the vertebral endplates are generally quite strong, it is desirable to preserve this structure even while removing portions of the bone. In the past, anterior interbody fusion would be performed by removing at least a portion of the intervertebral disc and then utilizing hand held instruments including, for example, osteotomes, chisels, curettes, rongeurs, and burrs to scrape and shape the vertebral endplates and vertebral bone stock. Such operations would be performed generally by working on one vertebra at a time, independent of the position of the adjacent vertebra.
Endplate preparation procedures can present the surgeon with several challenges. For example, the vertebral endplates should be prepared to match the implant to provide the greatest possible interface congruity between the endplates and the implant, as well as provide for the optimal contact surface, enhanced fusion area, and enhanced graft and construct stability. In order to achieve this, the amount of bone removed must be to a specified depth and width. Excess removal or penetration of the vertebral endplate can result in a weakening of the structural integrity of the vertebrae, thereby potentially causing the vertebral bodies to collapse around the fusion implant. Conversely, where an insufficient amount of bone is removed, blood flow may be very limited thereby hindering fusion of the implant to the vertebrae. This could potentially result in misalignment of the implant due to shifting.
Accordingly, there is a need for instruments and methods for the safe and effective preparation of adjacent vertebral endplates prior to a spinal fusion procedure.
The present invention provides a surgical bone preparation instrument useful during interbody fusion procedures, and methods of use thereof. The surgical bone preparation instrument is effective to remove a desired portion of bone from adjacent bone structures, such as vertebral endplates, to allow a sufficient amount of blood to flow to the implant, while maintaining the structural integrity of the vertebrae.
In general, the surgical bone preparation instrument includes a housing or sleeve member having an inner lumen or bore formed between a proximal end and a distal end. At least one distractor member protrudes distally from the distal end of the housing member and is adapted to be disposed between adjacent bone structures. The instrument further includes an elongate member, or rotatable cutting member, having a proximal end and a distal end. The proximal end of the elongate member can include a gripping surface, such as a handle, and the distal end of the elongate member includes a cutting element. The elongate member is adapted to be at least partially disposed within the inner lumen of the housing, such that the cutting element is positioned proximate to the distractor member. In use, the elongate member is rotated with respect to the housing, thereby causing the cutting element to penetrate and remove bone from the adjacent bone structures.
In one embodiment, the cutting member includes first and second opposed blade members effective to remove a portion of a surface of a bone structure upon rotation of the elongate member. The blade members are longitudinally oriented and include distal and proximal ends with a cutting surface extending therebetween. The cutting surface of each blade member can include first and second opposed leading edges which are effective to remove a portion of bone upon rotation of the elongate member in both a first direction and a second, opposite direction. The size, shape, and position of the blade members can be adapted to remove a specific region and amount of bone from the vertebral endplates. For example, the first blade member can be disposed distal of the second blade member to remove diametrically opposed regions of bone from the endplates.
In another embodiment, the instrument can include a rotation limiting element which defines a cutting path for the cutting member. The rotation limiting element can be formed from a slot disposed in the housing and extending over a portion of a circumference of the housing. An engaging element, such as a pin member, can be disposed on the rotatable cutting member such that the pin member is adapted to be disposed within the slot in the housing. In use, the shape of the slot defines a cutting path extending over a portion of the circumference of the sleeve member. For example, where the slot extends over 90xc2x0 of the circumference of the housing, the elongate member can be rotated 90xc2x0 in a first direction, and 90xc2x0 in a second, opposite direction thereby causing the first blade member to remove bone from a first vertebral endplate, and the second blade member to remove bone from a second, adjacent vertebral endplate.
In yet another embodiment, the housing component can include a stop member effective to prevent the housing from entering a space between adjacent bone structures. By way of non-limiting example, the stop member can be formed from a flange or shoulder that extends radially outward from the housing and is oriented substantially perpendicular to a longitudinal axis of the instrument.
In order to prepare adjacent bone structures, and more specifically the endplates of adjacent vertebral bodies, the distractor of the surgical bone preparation instrument is inserted between the bone structures to separate the adjacent vertebrae. The elongate member is then rotated, thereby causing the cutting element to remove a portion of bone from the endplate of each vertebra.